The availability of various alternatives for producing electricity, cooling, and heating enables a plurality of solutions to a given facility's needs. For example, there are available gas turbines and steam generators that may be used singly or in combination to produce electricity, and that generate byproduct thermal output (e.g., steam). Absorption chillers represent another advance, as they enable the production of a cooling fluid by using steam to create compression rather than electricity as used by conventional compressors.
The ready availability of natural gas and electric power supplies (as well as other power sources) to large scale facilities presents an opportunity for improved economics. In particular, it has become possible for a plant to adjust its reliance on each in light of changing prices. For example, a given plant may include a boiler system for providing heat using natural gas, coal or other fuel, a gas or fuel oil turbine for producing electricity, an absorption chiller for providing cooling, an electric compressor for providing cooling, and a connection to an electric grid for providing electricity purchased from a power plant. Such systems are known as cogeneration systems or, alternatively, CHP (cooling, heating, power) systems. The use of CHP systems presents an opportunity to modulate the amounts of electricity and fuel that are purchased and used for plant operations. However, control of such systems is complicated by their size and the plurality of factors that change over time, including maximum and minimum capacities, efficiencies, thermal and power loads, and prices. A stable and efficient control system is desired.